Block Island Southeast Light is a lighthouse located on Mohegan Bluffs at the southeastern corner of Block Island, Rhode Island. It was designated a U.S. National Historic Landmark in 1997 as one of the most architecturally sophisticated lighthouses built in the United States in the 19th century.

Although Congress appropriated $9,000 to build this light in 1856, the funds were used to build a new Block Island North Light after the old one was washed away in a storm. This light was finally built in 1874, with the lamp first lit on February 1, 1875. It is a sophisticated expression of the Gothic Revival executed in brick, and was a marked contrast to earlier lighthouses, which were generally more functional in appearance. The main tower is 67 feet (20 m) in height, with an octagonal granite foundation and brick exterior, which rises to a cast iron parapet and open gallery around the lantern chamber. This is topped by a sixteen-sided pyramidal copper roof with a ball ventilator and lightning rod. The original roof was cast iron, and was replaced in 1994.

The keeper's house is attached to the tower by a 1-1/2 story connecting wing. It is a 2-1/2 story brick structure with identical projecting 1-1/2 story kitchen wings at its rear, and a steeply pitched gable roof with windows extending into the roofline. There are porches on either side of the connector, one for each of the two dwellings in the building, which were originally identical. That on the southwest side has retained original trim, which includes beveled, bracketed posts. The north wing was designated for the keeper, while the south wing was for his assistants. The only major alterations to the residences have been for the introduction of modern plumbing (in 1938) and the repair of storm-related damage. The roof was originally shingled, and since has been covered by a variety of materials, most recently slate shingles.

The original optic was a first order Fresnel lens standing about 12 feet (3.7 m) tall with four circular wicks burning lard (pig) oil. The lard oil was replaced by kerosene in the 1880s. The lens was modified in 1929 to rotate floating on a pool of mercury, at first driven by a clockwork mechanism, which was replaced by a small electric motor.

In 1990, the Coast Guard deactivated the light and replaced it with a nearby steel tower. Because of ongoing erosion of the bluffs, in 1993 the entire 2,000 ton structure was moved about 300 feet (91 m) back from the cliffs. After the move, the Coast Guard decided not to retain the rotating mercury float lens, but instead installed the first order fixed lens which had been removed in 1980 from the Cape Lookout Lighthouse. Ownership of the lighthouse was transferred in 1992 to the Southeast Lighthouse Foundation, which is dedicated to its preservation.

The light was listed on the National Register of Historic Places in 1990, and designated a National Historic Landmark in 1997. The latter designation was made in recognition of the light's historic importance as an aid to navigation, and for its sophisticated architecture, which was only matched by the Cleveland Light, which was demolished in the early 20th century. As of its 1997 designation, it was one of only 12 lighthouses which used a first-order Fresnel lens.

The Southeast Lighthouse Foundation, which owns and manages the lighthouse, has filed lawsuits to block offshore wind farms. The organization has argued that offshore wind farms harm "our ocean view."

The lighthouse has a small museum and gift shop in the base of the tower. The tower is open during the summer season offering guided tours to the top, for a fee of $15 as of June 2024. Proceeds from tours are used for restoration of the lighthouse.

Keeper	years	First Assistant	years	Second Assistant	years	Special Assistant	years
Henry W. Clark	1875-1887	J. W. Tougee	1873-1874
		Nathaniel Dodge	1874-1882	Charles E. Dodge	1874-1882	Uriah B. Dodge	1879-1907
				John F. Hayes	1882
		John F. Hayes	1882-1883	Silas H. Littlefield	1882-1883
				Charles F. Milliken	1883
		Charles F. Milliken	1883-1886	Simon Dodge	1883-1886
		Simon Dodge	1886-1887	Willet H. Clark	1886-1887
Simon Dodge	1887-1922	Willet H. Clark	1887-1921	Charles E. Wescott	1887-1905
				Everett A. Hoxsie	1905-1907	Elmer H. Day	1907
				William A. Baker	1907-1908	Everett A. Hoxsie	1907-1912
				George L. Hoxsie	1908-1911
				Louis F. Schlett	1911-1912
				Samuel Pickup	1912-1917	Unknown, position possibly eliminated	1912-1990
				Ezra Dunn	1917-1918
				Edward Murphy	1918-1919
				Lawrence H. Congdon	1920-1922
		Lawrence H. Congdon	1922	John H. Miller	1922-1923
Willet H. Clark	1922-1930	Charles M. Ball	1922-1927
				Carl F. W. Anderson	1923-1924
				Percy L. Oppel	1924-1925
				Hugo R. Carlson	1926-1931
		Earl E. Carr	1927-1938
Carl F. W. Anderson	1930-1938
				Elmer F. O'Toole	1931-1935
				Charles A. Rogers	1935-1937
				Roger H. Green	1938
Earl E. Carr	1938-1943	Elmer F. O'Toole	1938-1941	Alfred L. Bennett	1939-1941
		Earl A. Rose	1941
		Unknown	1941-1990	Unknown	1941-1990
Unknown	1943-1946
Arthur Gasper	1946-1947
Unknown	1947-1948
Howard Beebe	1948-1950
John William Collins	1955-1959 OinC EN1 Fred Eidson, first assistant; BM3 Fred Gallop, second assistant; EN3 Don Goguen 1962

• Block Island North Light
• List of National Historic Landmarks in Rhode Island
• National Register of Historic Places listings in Washington County, Rhode Island

• Southeast Lighthouse Foundation
• Historic American Engineering Record (HAER) No. RI-27, "Block Island Southeast Light, Spring Street & Mohegan Trail at Mohegan Bluffs, New Shoreham, Washington County, RI", 53 photos, 12 measured drawings, 55 data pages, 4 photo caption pages
• SAH Archipedia Building Entry

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  Southeast Light looking NW ca. 1890
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  Aerial view of Southeast Light Station by U.S. Coast Guard, Salem, 1962
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  Southeast Light ca. 1988
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  Block Island Southeast Light
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  Block Island South East Lighthouse during sunrise in Shoreham, Rhode Island, USA. Photography by - Barry Mullin